Most songwriters hope their musical breakthrough will come in their younger years, but a 96-year-old widower from Illinois has proved it's never too late after the love song he wrote to his late wife made him an internet sensation and rocketed into America's iTunes top 10.

Fred Stobaugh's song Oh Sweet Lorraine has racked up more than 500,000 hits on YouTube and is rivalling the likes of Miley Cyrus and Lady Gaga in the US charts.

Stobaugh's wife Lorraine died in April aged 91, just shy of their 73rd wedding anniversary. After seeing a local singer-songwriter competition advertised in the newspaper, Stobaugh decided to try his luck and delivered his handwritten lyrics by post, while the other contestants sent in videos on YouTube.

Fred Stobaugh's wife, Lorraine. Photograph: YouTube

He did not win first prize, but the organisers decided to set the song to music.

Jacob Colgan, who owns the Green Shoe studio where the original competition was held, sings the lyrics that Stobaugh wrote. "Oh sweet Lorraine, I wish we could do the good times all over again," he croons.

In a YouTube video, Stobaugh is filmed holding back the tears as he listens to the recording of his song for the first time.

"She was just the prettiest girl I ever saw," he says in a YouTube documentary that has received over 1.6m views. "Real timid-like … I fell in love with her right there."